1. Field of the Invention
The invention relates to a method and device for monitoring intraocular pressure. Intraocular pressure, the pressure of fluid within an eye, takes on significance with respect to glaucoma and its treatment.
The glaucomas are a group of diseases that constitute a public health problem of staggering proportions. An estimated 5-10 million Americans have an intraocular pressure (IOP) greater than 21 mm Hg on routine office testing, placing them at increased risk of suffering glaucomatous optic nerve damage. Conservatively estimated, approximately 2 million Americans have glaucoma, while only 1 million patients are undergoing treatment. Nine hundred thousand Americans have some degree of vision impairment, and 80,000 patients are legally blind as a result of glaucoma.
Many factors are known to influence IOP, which accounts for the wide fluctuations noted in both the normal and glaucomatous population. Diurnal variation in IOP may frequently reach 6 mm Hg, and daily pressure peaks may reach 30 mm or more. Pressure spikes resulting from eye squeezing or rubbing can reach much higher levels. These pressure peaks may not be detected clinically, thus resulting in misdiagnosed, or undiagnosed glaucoma. Some glaucoma patients carry the diagnosis of normal tension glaucoma. While this group of diseases may represent an abnormal sensitivity of the optic nerve to seemingly normal IOP, it may also represent an inadequate sampling of IOP, which misses periods of significant IOP elevation. Thus, at least a subgroup of glaucoma patients may not be diagnosed, or treated, until a significant progression in their disease has been detected. The optimal frequency for measuring IOP has yet to be determined. Routine office visits are often spaced 3-4 months apart. Visits are more frequent during periods of medication adjustment. Following eye surgery, IOP measurements may be required every few hours. More than 3 million office visits each year are devoted to monitoring IOP in patients who are either being treated for glaucoma, or who are suspected of having glaucoma. Substantial healthcare resources are devoted to the task of monitoring IOP, and even this effort may represent a sub-optimal surveillance strategy.
2. Description of the Related Art
As a physiological parameter, IOP is important in its correlation with ocular fluid mechanics, muscular action, hemodynamics, and glaucoma diseases. For over three decades, medical, biomedical, and engineering professionals have been developing methods, devices and instruments to obtain accurate measurements of dynamic intraocular pressure. Conventional ophthalmotonometers (COT) are useful to this end, but, in general, they do not offer the features desired for certain ocular research and therapy. The medical needs are to continuously and xe2x80x9cconvenientlyxe2x80x9d monitor internal-to-the eye hydrostatic pressure in ambulatory subjectsxe2x80x94these attributes are lacking in COT.
One of the earliest attempts to obtain accurate measurements of intraocular pressure by direct contact with the internal fluids of the eye is described by Collins, Miniature Passive Transensor for Implanting in the Eye, IEEE TRANSACTIONS ON BIO-MEDICAL ENGINEERING, Vol. BME-14, No 2, April 1967.
Work in this area during the following two decades indicates the continued need for and interest in obtaining dynamic, real-time intraocular pressure measurements. Few of the advances in this area take a direct measurement of the eye""s internal pressure, that is, by having the hydrostatic pressure of eye fluids acting directly on a sensor. In most cases, IOP was inferred using various active and passive pressure sensors in contact with the external globe, sclerotic or cornea, of the eye. Examples of active pressure sensors include strain gauge type sensors. Examples of passive pressure sensors include self-resonant type sensors.
More recent efforts are described in Schnell et al., xe2x80x9cMeasurement of Intraocular Pressure by Telemetry in Conscious Unrestrained Rabbits,xe2x80x9d INVESTIGATIVE OPHTHALMOLOGY and VISUAL SCIENCE, Vol. 37, No. 6, pp. 958-965, May 1996, and McLaren et al., xe2x80x9cContinuous Measurement of Intraocular Pressure in Rabbits by Telemetry, xe2x80x9d INVESTIGATIVE OPHTHALMOLOGY and VISUAL SCIENCE, Vol. 37, No. 6, pp. 966-975, May 1996. Schnell and McLaren utilized technology commercially available from Data Sciences International of St. Paul, Minn., to obtain hydrostatic IOP within the midvitreous and aqueous humor, respectively.
The present invention provides a method and apparatus for directly and continuously monitoring intraocular pressure.
The present invention concerns a device for measuring intraocular pressure (IOP) of a patient (an IOP monitoring system). The IOP monitoring system includes an in vivo sensor. The sensor includes a capacitive pressure sensor and an inductive component. An excorporal (external to the patient) instrument remotely measures the pressure in the eye, provides readout of pressure values and energizes the sensor, thereby permitting the instrument to determine the intraocular pressure.
Additionally, the present invention relates to a method for measuring intraocular pressure of a patient. A signal is generated with an instrument external to the patient for remotely energizing an in vivo sensor. Interaction between the signal produced by the instrument and the sensor is measured. The interaction is correlated with intraocular pressure.
Still other objects and advantages of the present invention will become readily apparent by those skilled in the art from the following detailed description, wherein it is shown and described in the preferred embodiments of the invention, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of different embodiments and its several details are capable of modifications in various obvious respects, without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive.